[examancer]

CoffeeScript was never the "default". Since the asset pipeline was added new rails projects contained only a single 'application.js' which included any default JS libs. There has never been coffeescript in a default rails project. That makes the default plain-old JavaScript. CoffeeScript has just been there as a default gem so it was available to you by default, but you have never been forced or even strongly encouraged to use it.

That said, I love CoffeeScript and continue to use it to this day. It gets a lot of hate and I've been pushed to write a lot of ES6 these days, but CoffeeScript is still much more succinct.